1. Field of the Invention
The present invention relates in general to a brake pedal apparatus, and more particularly to such a brake pedal apparatus having a high degree of freedom in setting of a lever ratio characteristic.
2. Discussion of Prior Art
There is known a brake pedal apparatus having (a) an operating pedal which is disposed pivotably about a first axis, (b) a pivot member which is disposed pivotably about a second axis parallel to the first axis, and which is connected to the operating pedal via a link mechanism so as to be mechanically pivoted about the second axis in response to a depressing operation effected on the operating pedal; and (c) an output member which is to be mechanically pressed or pulled as a result of pivot motion of the pivot member. As an example of such a brake pedal apparatus, Patent Document 1 discloses an apparatus in which a lever ratio representative of a ratio of an output to a depression force acting on the operating pedal is changed in accordance with a pedal stroke.
Patent Document 1: JP-H7-205776A
Patent Document 2: JP-H10-29510A
However, in such a conventional brake pedal apparatus, since a characteristic of change of the lever ratio (lever ratio characteristic) is dependent on connected positions of the link mechanism, it is difficult to largely change the lever ratio halfway during the pedal stroke. Thus, the change in the lever ratio is not necessarily satisfactory.
Patent Document 2 discloses a technique of largely changing the lever ratio characteristic by changing a path for transmission of the depression force. According to an arrangement disclosed by this document, in a normal case, the depression force is transmitted from the operating pedal to an input rod of a brake booster via an elastic member. When the depression force applied to the operating pedal is increased, for example, in the event of failure of the brake booster, the depression force is transmitted from the operating pedal directly to the input rod of the brake booster. However, the disclosed arrangement is for changing the lever ratio characteristic in accordance with the depression force, rather than for largely changing the lever ratio in accordance with the pedal stroke during a normal operation of the operating pedal. Further, since the elastic member is arranged to receive the depression force at its portion that is offset from the input rod of the brake booster, the input rod can be easily stuck, thereby causing a risk of deterioration in efficiency of transmission of the depression force and durability of the brake pedal apparatus.
The present invention was made in the light of the background art discussed above. It is therefore an object of the invention to provide a brake pedal apparatus which is capable of changing the lever ratio by a large amount halfway during the pedal stroke without considerable deterioration in the efficiency of transmission of the depression force and the durability of the apparatus, and which has a high degree of freedom in setting of the lever ratio characteristic.